1. Field of the Invention
The present invention relates to a technique for a conversion process for optimizing RGB image data for printing in a printing system for commercial printing.
2. Description of the Background Art
The proliferation of digital cameras has increased the so-called submission of RGB originals, that is, the transfer (or submission) of layout data for use as an original for printing to a prepress/printing process step, the layout data being created using a photographic image which is an image (RGB image) captured by a digital camera and represented in the RGB color system. RGB image data which provides an RGB image is incorporated (or described) in accordance with a predetermined format in layout data submitted in the form of an RGB original. In the prepress/printing process step, however, it is necessary to perform a color space conversion process for converting the RGB image data into CMYK image data which provides a printable image (CMYK image) represented in the CMYK color system.
Graphic images including graphs created using spreadsheet software or presentation software and so-called CG (computer graphics) images created using drawing software are also created in the form of RGB images. The submission of RGB originals as originals for printing in which such graphic and CG images are arranged in the form of the RGB images for layout has also been on the increase.
The layout data is created, for example, as PDF (Portable Document Format) data. When the layout data is described in the PDF, the color space conversion process is performed on all images arranged for layout by one operation, based on an ICC profile embedded as header information in the layout data.
However, the ICC profile is originally used to maintain color reproduction between input/output devices having different color reproduction characteristics, and the color space conversion process based on the ICC profile is performed uniformly on all image data incorporated in the layout data. Thus, the color space conversion process neither reflects conventional conversion processes (gamut mapping) which have been done by a scanner operator based on his/her empirical rules, nor carries out an sharpness process. On the other hand, it is a common practice that a plurality of images are arranged for layout on printed matter. Individual images different in type (photographic, graphic, or CG images) and in what they express necessitate different processes of image correction to be performed for improvements in expressiveness thereof. To achieve high-quality printed matter, there arises a need to individually perform such image correction processes on a plurality of pieces of image data which provide the individual images in the prepress/printing process step.
To satisfy the need, a printing system (RGB image quality control system) to be described below has been accomplished. In this printing system, recipe data, indicative of the details of the color space conversion process and the image correction process which are image processing to be performed on each RGB image in the prepress/printing process step, is incorporated (or described) during a layout operation in a production/design process step into the layout data described in the PDF and including photographic data providing the RGB images. Then, in the prepress/printing process step, the printing system interprets the details of the recipe data to perform a necessary process, and thereafter performs a rasterizing process or other processes.
If only the image conversion process based on the ICC profile is performed on the layout data received in the form of the RGB original, it is necessary to perform the above-mentioned image correction process on the individual pieces of RGB image data incorporated in the layout data in the prepress/printing process step. However, an output process has become more automated in the recent prepress/printing process, as represented by an intelligence workflow RIP system, and the setting of parameters regarding the output process has become a main operation in the prepress/printing process step. Thus, the above-mentioned correction process is incompatible with the more automated output process.
There is another problem to be described below. Not only the conversion process from the RGB image data to the CMYK image data but also the image correction process to be performed on the original for printing for the purpose of providing high-quality printing has conventionally been performed in a quite different process step than the prepress/printing process step. Therefore, there are not a sufficient number of operators skilled in such processes in the prepress/printing process step.
The use of the above-mentioned RGB image quality control system solves the aforementioned problems in the prepress/printing process step. However, in the RGB image quality control system, equipment for the production/design process step which is a sender of the layout data must have special software capable of creating the recipe data prior to the layout of printed matter. The layout data subjected to such a special process are not always created in the production/design process step.